System and method of virtual modeling of thin materials

ABSTRACT

A virtual model capable of simulating physical deformation of at least a portion of a product to be worn on a body. The portion comprises a thin, flexible material, wherein the model comprises a first zone of compression defining two major surfaces, wherein at least one of said major surfaces further comprises a zone of bending.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/550,479, filed Mar. 5, 2004 and U.S. Provisional Application No.60/550,490 filed Mar. 5, 2004.

FIELD OF THE INVENTION

The present invention relates to three-dimensional computer-aidedmodeling and design of garments to be worn on a body.

BACKGROUND OF THE INVENTION

Computer simulations of motion, e.g., using FEA, have long been used tomodel and predict the behavior of systems, particularly dynamic systems.Such systems utilize mathematical formulations to calculate structuralvolumes under various conditions based on fundamental physicalproperties. Various methods are known to convert a known physical objectinto a grid, or mesh, for performing finite element analysis, andvarious methods are known for calculating interfacial properties, suchas stress and strain, at the intersection of two or more modeledphysical objects.

Use of computer simulations such as computer aided modeling in the fieldof garment fit analysis is known. Typically, the modeling involvescreating a three-dimensional (hereinafter “3D”) representation of thebody, such as a woman, and a garment, such as a woman's dress, andvirtually representing a state of the garment when the garment isactually put on the body. Such systems typically rely on geometryconsiderations, and do not take into account basic physical laws. Onesuch system is shown in U.S. Pat. No. 6,310,627, issued to Sakaguchi onOct. 30, 2001.

Another field in which 3D modeling of a human body is utilized is thefield of medical device development. In such modeling systems, geometrygenerators and mesh generators can be used to form a virtual geometricmodel of an anatomical feature and a geometric model of a candidatemedical device. Virtual manipulation of the modeled features can beoutput to stress/strain analyzers for evaluation. Such a system andmethod are disclosed in WO 02/29758, published Apr. 11, 2002 in thenames of Whirley, et al.

Further, U.S. Pat. No. 6,310,619, issued to Rice on Oct. 30, 2001,discloses a three-dimensional, virtual reality, tissue specific model ofa human or animal body which provides a high level ofuser-interactivity.

Also, U.S. Pat. No. 6,810,310 discloses methods for modeling products tobe worn on a body. However, this patent does not provide any disclosuredirected to specific product features and how they can be modeled.

The problem remains, therefore, how to model fit of a specific garmentfeatures in a virtual environment.

Further, there is a need to model fit of a specific garment features ina virtual environment in both static and dynamic conditions whilecalculating physics-based deformations of either the body or thegarment. The problem is complicated more when two deformable surfacesare interacted, such as when a soft, deformable garment is in contactwith soft, deformable skin.

Further, there remains a need for a system or method capable of modelingspecific product features of a soft, deformable garment, particularlywhile worn on a soft deformable body consistent with fundamental laws ofphysics.

Further, there remains a need for a system or method capable of modelingsoft, deformable garment features, particularly while worn on a softdeformable body under dynamic conditions, such as walking or the act ofsitting that simulates real stress/strain behavior.

Finally, there remains a need for a system or method capable of modelingsoft, deformable garment features, particularly while worn on a softdeformable body under dynamic conditions that is not overlycomputer-time intensive; that is, it does not require such time andcomputing capability as to make it effectively un-usable for routinedesign tasks.

SUMMARY OF THE INVENTION

A virtual model capable of simulating physical deformation of at least aportion of a product to be worn on a body is disclosed. The portioncomprises a thin, flexible material, wherein the model comprises a firstzone of compression defining two major surfaces, wherein at least one ofsaid major surfaces further comprises a zone of bending.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart depicting schematically one embodiment of asystem of the present invention.

FIG. 2 is a depiction of a point cloud.

FIG. 3 is a schematic representation of two defined volumes.

FIG. 4 is another schematic representation of two defined volumes.

FIG. 5 is a meshed, three-dimensional model of a portion of a body.

FIG. 6 is a meshed, three-dimensional model of a garment to be virtuallyprototyped by the system and method of the present invention.

FIG. 7 is a schematic representation of solid elements and a shell.

FIG. 8 is plan view of a garment having elastic elements modeled.

FIG. 9 is a detail view of a portion of an elastic element modeled on agarment.

FIG. 10 is another detail view of a portion of an elastic elementmodeled on a garment.

FIG. 11 is plan view of a garment having elastic elements modeled.

FIG. 12 is a detail view of a portion of an elastic element modeled on agarment.

FIG. 13 is a detail view of a portion of an elastic element modeled agarment.

FIG. 14 is detail view of a portion of an elastic element modeled on agarment.

FIG. 15 is a perspective view of a garment model modeled on a bodymodel.

FIG. 16 is a schematic representation of a model for modeling a fold.

FIG. 17 is a schematic representation of a model for modeling a seriesof folds.

FIG. 18 is a perspective view of a product model going through severalsteps of folding.

FIG. 19 is a perspective view of a folded product model going throughseveral steps of unfolding.

FIG. 20 is a perspective view of several steps in the model of applyinga garment model to a body model.

DETAILED DESCRIPTION OF THE INVENTION

The virtual model of the present invention can be used to virtuallymodel the dynamic behavior of a body, such as a human body, and thebody's interaction with garments. As used herein, the term “garments”means any article or object intended for placement on or in the body andintended for temporary wear. Therefore, the term garments includesexternally-worn articles, such as clothing including hats, gloves,belts, shirts, pants, skirts, dresses, thermal wraps (that can be wornover other clothing) and the like. The term garments also includesinternally-worn articles such as earplugs, hearing aids, mouth guards,and tampons. Internally-worn articles generally have externally-disposedaccess means for placement and removable, such as finger extensions onearplugs and strings on tampons. Some garments can be partially externaland partially internal, such as earrings in pierced ears, hearing aidshaving externally-disposed portions, and interlabially-placed catamenialdevices.

It is believed that the method and system of the present invention isbest suited for designing garments intended for close body contact, suchas shoes, gloves, brassieres and other intimate garments. In a preferredembodiment of the present invention a three-dimensional, virtual body isutilized to model the crotch region of a human woman and a sanitarynapkin garment. The invention is not limited to such a person orgarment, however, and it may be used for modeling the interaction of anygarment/body interface, particularly under dynamic conditions. In thepresent invention, whether externally-worn, internally-worn, or acombination thereof, virtual modeling is used to simulate wear based onfundamental physical laws.

The invention can be understood by following the steps discussed belowin conjunction with the flowchart in FIG. 1. The flowchart of FIG. 1depicts elements associated with the virtual model of the invention,starting with the step of generating an image of a body, or a portion ofa body to be surfaced. Surfacing is a technique for rendering a computergenerated three-dimensional (3D) image of an actual 3D object. In oneembodiment the portion of the body to be surfaced is the waist region ofa human, including the crotch area and pudendal region, of an adultfemale. In another embodiment, the waist region is the waist region ofan infant, useful for modeling disposable diapers. If the model is to beused to model a garment, the surfaced portion of the body includes thatwhich is to be modeled with a garment.

Surfacing of a body can be achieved by means known in the art, such asby imaging the external surface of a portion of a body by making aseries of images of the desired portion of the body using surfacedigital imaging techniques. However, in a preferred embodiment,surfacing of portions of a human body can be achieved by imagingtechniques that also capture internal portions, such as magneticresonance imaging (MRI). Other techniques for obtaining suitable imagesfor surfacing could be used, such as ultrasound imaging or x-rayimaging, but MRI scans have been found to be preferred in the presentinvention.

The resolution of the MRI images will determine the level of detailavailable for analysis of fit. Therefore, the MRI scan should havesufficient resolution, including a sufficient number of “slices,” tocapture anatomical features relevant to fit and comfort for the garmentbeing modeled. The term “slices” is used in its ordinary sense withrespect to MRI scans, and denotes the two-dimensional images produced byMRI imaging. In one embodiment, coronal slices of the waist region of anadult female were imaged with a 2 mm (1:1 scale) increment resolutionusing a GE Medical Systems Genesis Sigma 1.5 Echo Speed LX MRI unit. Thedata output can be a series of DICOM image files that can be exportedfor further evaluation and analysis. The DICOM image files can havemultiple regions corresponding to various components or tissues of thebody. For example, each slice of an MRI image may show regions of fat,skin, muscle, bone, internal organs, and the like. For the purposes ofthe preferred embodiment of a sanitary napkin, the regions of skin, fatand muscle in the pudendal region are of the most interest.

A point cloud representation can be made from the DICOM image files. Oneach slice of MRI images, the various regions, and the interface betweenregions can be located and designated by a series of points which can beidentified and designated by either the software or manually by theuser. The points so designated create a point cloud representation ofeach slice of MRI image. The number, concentration, and spacing of thepoints can be chosen to get sufficient resolution for the body portionbeing modeled, such as sufficient resolution to capture the undulationsof tissues, e.g., the skin, in the various regions. In general, thenumber of points and their spacing should be such that relevant bodyportions are accurately represented to a sufficient resolution relevantto fit and comfort. In one embodiment, a distance of about 2 mm (1:1scale) between points of the point cloud was found to provide sufficientresolution for analyzing fit and comfort of a garment worn on a body.

Once the points on each two-dimensional MRI slice are placed, software,such as the sliceOmatic® software referred to above, can generate athree-dimensional point cloud based on the relative position of the MRIslices. Once the three-dimensional point cloud is obtained, the data canbe stored in electronic format in a variety of file types. For example,the point cloud can include a polygonal mesh in which the points areconnected and the point cloud can be saved as a polygonal mesh file,such as a stereolithography file, that can be exported for furtherevaluation and analysis. An example of a visual rendering of a 3D pointcloud 12 for the waist and crotch region 10 of a human female is shownin FIG. 2.

The point cloud of the body portion can then be surfaced by utilizingsuitable software, including most computer aided design (CAD) softwarepackages, such as, for example, Geomagic® available from RaindropGeomagic (Research Triangle Park, N.C.). Surfacing can also be achievedby any of various means known in the art, including manually, ifdesired. In a preferred embodiment particular regions of the body can besurfaced, such as the interface between fat and muscle, fat and skin,and/or muscle and bone.

Once the body portion of interest is surfaced, the specific body portionof interest to be modeled is determined. For example, when modelingsanitary napkin garments, the body portion surfaced may be the entirewaist and crotch region of an adult female, while the body portion ofinterest to be modeled is the pudendal region. The body portion ofinterest to be modeled is the portion of the body in which deformationsare to be measured to model comfort and fit.

After determining the body portion of interest to be modeled, thesurfaced portion can be arbitrarily partitioned into at least twovolumes to isolate in one volume the body portion of interest to bemodeled, i.e., portion of the body that is to remain deformable duringmodeling based on physics-based criteria. The remainder of the surfacedvolume can simply be modeled by prescribed motion, thereby conservingresources in computing time. In a preferred embodiment, the surfacedbody is partitioned into two separate, non-intersecting volumes,including at least a first deformable volume, and at least a second aprescribed motion volume. By “deformable volume” is meant a volume inwhich, when the simulation is performed, e.g., via finite elementanalysis (FEA), physical behavior, e.g., stress, deformation and motion,are computed. Conversely, by “prescribed motion volume” is meant avolume in which the deformations and motions are dictated by input tothe simulation, and are not computational outputs of the simulation.

The prescribed motion volume is used to ensure realistic garment fit andpositioning, but otherwise can have little impact on the physics-basedanalysis of body fit and comfort for the garment under evaluation. Thatis, the prescribed motion volume represents areas in which the garmentmay or may not interact with the wearer, or, where interaction is oflesser interest for a particular fit analysis. In general, the extent ofthe prescribed motion volume, and, likewise, the deformable volume, canbe varied to obtain optimum results, depending on the specific garmentbeing analyzed. For example, in the preferred embodiment of a sanitarynapkin, the portion of the body corresponding to the pudendal region ofa female, including interior anatomical features, can be rendereddeformable as one volume, while the remaining portions of the body arerendered as a separate, non-deformable volume.

By “non-intersecting” with respect to the two volumes of the preferredembodiment is meant that the volumes do not overlap, i.e., no portion ofthe modeled body consists of both the deformable volume and theprescribed motion volume, but the two volumes are distinctlypartitioned. In one embodiment, only the deformable volume need bedetermined, and then, by definition, the remainder of the body portionto be modeled represents the prescribed motion volume. The two volumescan share a common surface interface, which is all or a portion of theirrespective surfaces shared between the two volumes.

As shown in FIG. 3, interfacial surface 24 can be fully interior to thesurfaced body portion 12, i.e., a surface defined as being a certaindistance “in,” so to speak, from the external surface 20. The distance“in” should be great enough so as to allow for the external surface 20to be deformable when modeled. Further, the interfacial surface shouldbe in sufficient proximity to the external surface so as to be capableof driving motion of at least a portion of the external surface. In theembodiment shown in FIG. 3, interfacial surface 24 defines prescribedmotion volume 26 which is “inside” deformable volume 22 and forms nopart of the external surface 20 except at the cross-sections of the bodyportion 12.

As shown in FIG. 4, interfacial surface 24 can extend to and bepartially bounded by a portion of the external surface 20. In FIG. 4,deformable volume 22 and prescribed motion volume 26 meet at interfacialsurface 24 that extends to external surface 20. FIG. 4 shows two volumesthat have been found to be useful for modeling feminine hygiene devices,such as sanitary napkins. As shown, a deformable volume 22 correspondsto the body portion of interest to be modeled, in this case the pudendalregion of an adult female for evaluation of a sanitary napkin garment.Likewise, a prescribed motion volume 26 corresponds to the portions ofthe body not of interest for comfort and fit of the sanitary napkin, buthelpful to understand and simulate overall body movement.

After partitioning into volumes is complete, the surfaced andpartitioned body portion(s) can be meshed. From the surfacing software,such as Geomagic®, the surfaces can be imported into software capable ofrendering the surfaces in three dimensions, such as I-DEAS® availablefrom UGSPLM Solutions, a subsidiary of Electronic Data SystemsCorporation (Plano, Tex.), through an IGES file format. Using I-DEAS®,the surfaces are used to generate 3D renderings defining correspondingseparate components corresponding to the tissues in the portions of thebody to be analyzed, for example the fat, muscle, and bone. To generatethese 3D renderings, the technique of volume rendering from surfaces canbe used as is commonly known in the art.

The defined volumes can be meshed separately into a mesh of nodes andelements by means known in the art. For example, meshes can be createdcontaining solid elements, shell elements, or beam elements. In apreferred method of the present invention, the deformable volume ismeshed as solid elements as shown in FIG. 5. Various tissues within thedeformable volume, such as fat tissues, muscle tissues, and the like canbe meshed into separate parts, and each part can have appropriatematerial properties assigned to it, while maintaining the continuity ofthe mesh. As shown in FIG. 5, the body portion of interest, which isgenerally part of the deformable volume, can be meshed with a greaterdensity of nodes and elements.

The prescribed motion volume may be meshed as shell elements or solidelements, or no mesh at all, at least in some portions. The prescribedmotion volume need only be meshed sufficiently to enable realisticgarment positioning, in both static and dynamic conditions. Having thetwo volumes with different mesh properties allows for a significantreduction in the number of nodes and elements necessary to simulate thebody portion of interest. Those skilled in the art will recognize thatminimizing the number of nodes and elements directly correlates withreducing the cost of the simulation.

To do motion simulation and fit modeling it is necessary that motion ofthe body portion being modeled be driven, i.e., moved through space intime. In the present invention, motion is driven by driving at leastportions of the interfacial surface. Since the deformable volume issubject to physics based constraints, driving the interfacial surface inturn drives motion of the deformable volume that is free to move anddeform, with the deformations producing measurable stress and strain.The prescribed motion volume, as its name suggests, follows motioncurves consistent with the motion of the interfacial surface.

The measurable stress and strain can be due to contact with the garmentbeing modeled. Moreover, a series of garments can be tested in sequenceby using the same partitioned body portion, thereby enabling multiplegarments to be relatively quickly tested for fit or comfort.

The interfacial surface is driven along predetermined motion curves inspace and time. The predetermined motion curves can be generated by useof external motion capture or by manually selecting and inputting aseries of points in space and time. In another embodiment, thepredetermined motion curves are produced from kinematic animations usinganimation software, for example Maya® from Alias Wavefront. In akinematic animation a kinematic skeleton can be created and attached tothe interfacial surface. The user can then prescribe the motion of thekinematic skeleton through time. The animation software uses theprescribed kinematic motion to drive the motion of the interfacialsurface. Finally, the time dependent motion can be exported for all or aportion of the nodes on the interfacial surface. That is, the motioncurves can be assigned to only portions of the interfacial surface.

The garment to be evaluated in the virtual model of the presentinvention can be generated by producing a computer aided design (CAD)geometry of the actual garment of interest. CAD geometries can beproduced from CAD drawings, as is known in the art. Once the CADgeometry is produced, it can be meshed into a mesh of nodes and elementsby means known in the art. The number of nodes and elements can bevaried as necessary or desired for adequate garment modeling.

In one embodiment, the garment is a sanitary napkin intended to be wornagainst the body of an adult woman as shown in FIG. 6, which shows ameshed sanitary napkin garment. In most cases the sanitary napkin isworn inside the undergarment, such as elasticized panties. Therefore, inone embodiment of the present invention, the garment can actually be agarment system comprised of two or more garments interacting duringwear. For example, certain sports equipment, such as shoulder pads andjerseys can be analyzed for fit and comfort as a multiple garmentsystem. Likewise, the interaction between shoes and socks can beanalyzed.

The garment can be comprised of more than one structural component, andeach component can be created as a separate part and meshedindependently. This enables individual material properties to beassigned to each component. For example, a woman's undergarment can haveat least three components: the overall panty fabric, the crotch fabric,and the elastic strands. Each of these components can be created asseparate parts with individualized material properties appropriate foreach material. The material properties can be revised by the user asnecessary for different garments.

The garment can be modeled in various initial states, such as in arelaxed, undeformed state, or in a non-relaxed or deformed state. Forexample, a sanitary napkin can be initially modeled in a generally flat,undeformed initial state, as shown in FIG. 6, or it can be initiallymodeled in a bunched, folded state. In one embodiment, a garment isinitially modeled by having the fewest number of components initiallystressed. For example, sanitary napkin can be modeled in a flat-out,undeformed configuration.

Predetermined fixed points on the meshed garment, or garment system, canbe identified, the fixed points being fixed in space or with respect tothe meshed body during fit analysis according to the present invention.In general, the fixed points can be a maximum distance from thedeformable volume of the meshed body.

The fixed points aid in the garment being “applied” to the meshed bodyby using motion curves to prescribe motion to the fixed points such thatthe fixed points are translated from a first initial modeled position toa second fixed position relative to the meshed body. To simulate fit andcomfort of the garment and body, respectively, the garment or garmentsystem is first “applied” as described above. At this point, thesimulation can calculate stresses and strains associated with fit priorto body motion. By driving motion of the body through the predeterminedmotion curves of the interfacial surface, dynamic stress-straincalculations on the deformable volume and garment or garment system canbe made and correlated with dynamic fit and comfort.

Fit and comfort analysis can be achieved by use of a dynamicstress-strain analyzer, such as, for example, LS-DYNA® (LivermoreSoftware Technology Corporation, Livermore, Calif.), ABAQUS® (ABAQUSInc., Pawtucket, R.I.), or, ANSYS® (ANSYS Inc., Canonsburg, Pa.). Anydesired inputs, such as body mesh motion, garment mesh motion, contactsurfaces, garment mesh, and/or body mesh can be inputted to accomplishthe analysis. The stress-strain analyzer supplies an output of deformedmotion and corresponding forces, such as stress and strain. The forcesinclude forces associated with deforming both the body and the garment.Garment deformation and the magnitude of the forces required to generatethe deformation can be correlated to fit and comfort.

Optionally, the simulation output, such as deformations and forces canalso be visualized using software such as LS-PREPOST® (LivermoreSoftware Technology Corporation, Livermore, Calif.), Hyperview® (AltairEngineering, Troy, Mich.), Ensight® (Computational EngineeringInternational, Apex, N.C.), or ABAQUS VIEWER® (ABAQUS Inc., Pawtucket,R.I.), for example. Visualization of the garment as the body portion ismanipulated can show in visual representation the deformation of thegarment. For example, a sanitary napkin can undergo buckling, twisting,and bunching during wear. Such deformation is difficult, if notimpossible, to watch in real time on a real person due to the practicalconstraints of such a system. However, such pad fit characteristics canbe easily visualized and manipulated in the computer simulation. Thiscapability significantly reduces the time and expense of designingbetter fitting garments such as sanitary napkins. Properties ofmaterials can be changed as desired and inputted through the dynamicstress-strain analyzer to change the characteristics of the garment,thereby providing for virtual prototyping of various designs. Themethods, software and techniques disclosed above can be used inconjunction with standard modeling practices, including those disclosedU.S. Pat. No. 6,810,310.

Certain features of disposable absorbent articles and other soft,deformable garments and products can be modeled more efficiently by useof the methods and techniques disclosed below. These methods are usefulfor modeling disposable absorbent articles such as adult incontinenceproducts, disposable diapers, and sanitary napkins. These methods arealso useful for modeling other garments and disposable articles,including such products as ThermaCare® thermal wraps from The Procter &Gamble Co., or instant heat packs (disposable), such as infant heelwarmers available from The Kimberly-Clark Co. These methods are alsouseful for other consumer products such as Crest® Whitestrips oral careproducts, Swiffer® floor cleaning pads, and other consumer products suchas trash bags, ground covers, and the like.

Very thin structures, such as fibrous materials, nonwoven webs, polymerfilms, absorbent cores, paper webs, woven fabrics, and the like can bemodeled using only shells, as is well known in the art of finite elementanalysis modeling. It has been found in modeling of very thin structuresthat shell elements have a drawback of being unstable in simulationrequiring contact with other product features or a body. While suchshells can work well for modeling tensile and bending stresses, shellstructures cannot adequately handle compression through the thickness,and it is well known in the art that interaction with other features orcomponents at the edges of the shell presents a significant challenge.For similar reasons two dimensional openings such as slits and slotscontained within a structure built from a thin web pose similarchallenges. It has been found that much more stable virtual simulationscan be achieved by making thin structures using solid modeling elements,that is, model as a structure of 3-D solid elements having a shellsuperimposed thereon, as shown in FIG. 7.

It is believed solid elements can be in single layers or in multiplelayers as shown in FIG. 7, and aid in accurate modeling of compressionand edge interactions in contact, while the shell elements model bendingand tensile deformation more accurately. By “layer” is meant that theelements are each connected to adjacent elements by at least one node todefine a continuous structure. If a single layer of solid elements isused to model thin materials, the layer has two major surfaces, a topsurface and a bottom surface. These surfaces are considered as externalmajor surfaces. If more than one layer of solid elements is used throughthe thickness of the thin material, surfaces of adjacent solid elementsare considered as internal major surfaces. The shell can be superimposedon any of the major surfaces of the solid element layers including thetop surface or bottom surface or any internal major surface.

This approach permits the use of relatively simple material models tomodel far more complex material behavior with reasonable accuracy. Inone embodiment reasonable accuracy of thin, flexible materials could bemodeled using low density foam material models for the solid elementsand linear elastic material for the shell elements. However, any varietyof material models could be considered in this approach, including soilmaterial models, foam material models, elastic-plastic material models,linear elastic material model, hypereleastic material models, hyperfoammaterial models, and such.

To model a region of increased flexibility, such as slits, score lines,perforations, or the like, the shell surface in the regions of increasedflexibility can be removed. Because the shell can be the portion of themodel having greater bending resistance, once removed, that portion ofthe model exhibits an increased flexibility and less resistance tobending.

Another benefit to modeling with the solid/shell structure disclosedabove is that it can model sided bending behavior in thin materials. Bysided bending is meant that the bending force required to bend agenerally planar, flat material out of plane is different when bendingout of plane in one direction versus bending out of plane in the otherdirection. For example, when bending a generally flat material such as apiece of paper, nonwoven, polymer film, or laminates thereof into agenerally curved shape, one side is in tensile stress while the otherside is in compressive stress. If the stress of either tension orcompression differed depending on which way the material were bent, thematerial would be considered “sided.” Such behavior can be simulated inwhich the shell is intentionally placed on a surface which is not thesurface that runs through the middle of the thickness of the structure.For example, placing the shell on the bottom surface or top surfacewould capture such sided behavior. This amount of sided bending can beadjusted in considering modifications to the tensile modulus of thesolid elements.

In addition to modeling each material separately, a plurality ofmaterials can be modeled as a single structure having properties of thecomposite material. For example, an absorbent core laminated on one sidea polymer film, such as a backsheet. The absorbent core, laminationadhesive, and polymer film can be modeled as a composite structure usingthe technique above.

Another problem for modeling absorbent articles is the problem ofmodeling absorbent materials that collapse when wet. Absorbent corematerials, such as some cellulosic, airfelt, or fluff cores, typicallyhave a certain volume when dry, but when wetted, and subject to force,it does not recover to its original volume. This force can include theforce of gravity of the wetted material resulting in a gravity-drivenwet collapse. Modeling wet collapse, particularly in only a portion of acore material, e.g. the central region of a baby diaper core or asanitary napkin core, can be a problem.

One approach to modeling a portion of an absorbent that has beensaturated is to recognize that wet materials of the type used forabsorbent core have virtually no bulk recovery, that is, little or noamount of thickness recovery after wet collapse. This can be modeled inan absorbent product by defining certain portions of the absorbentproduct, such as central portions of the absorbent core as beingcrushable foam, such as *MAT_CRUSHABLE_FOAM available from LS-Dyna.Further, by recognizing that saturated absorbent structures exhibitlittle stiffness in bending, this potion of the absorbent structure canbe modeled as solid elements without shells underneath. In oneembodiment, a very small tensile modulus of 2 psi was used in the foammaterial model since the tensile modulus can potentially impact thebending stiffness.

The remainder of the absorbent material which is not saturated withfluid can be modeled either as described above, or with solid elementsor more generally with a single material model such as soil materialmodels, foam material models, elastic-plastic material models, linearelastic material model, hypereleastic material models, hyperfoammaterial models, and such. This can include modeling of features such aschannels, fold lines, embossments, fusion bonds, ultrasonic bondingpoints, seams, and other three-dimensional features, as well as othercomponents such as absorbent gelling materials and fibers.

Another element to model on garments to be worn on a body is elastic.For example, on undergarments, elastic often encircles the leg openingsand waist opening. On disposable diapers elastic elements are oftendisposed in waist regions and around leg openings and in barrier legcuffs.

Using a woman's undergarment, commonly referred to as a panty, as anexample, several methods of modeling elastic members can be disclosed.As shown in FIG. 8, a panty 30 is shown having leg and waist elasticmembers 32. In one embodiment, the elastic members 32 are modeled as aseries of square, pre-stressed components 34, that can be shellelements, that create contraction of the leg elastic. FIG. 8 shows thesquare elements as being pre-stressed, and FIG. 9 shows the sameelements in a relaxed mode.

As shown in FIGS. 9 and 10, the approach described above requires holes,or open spaces 36 to be modeled. The modeled holes can introduceinstabilities into the simulation. Therefore, in another embodiment,elastic members can be modeled as shown in FIGS. 11 and 12 aspre-stressed beam elements. This approach involves modeling the elasticmembers as shells 40 and running a series of pre-contracted beams 42along the edge of the shell elastics. In one embodiment, the shellelement was un-stressed and had a Young's modulus of 70 psi and the beamelements were pre-stressed with 75% extension in the longitudinaldirection and had a Young's modulus of 140 psi. While this approachresolves the issues of the square element approach above, it does havesome stability issues as well, as the pre-stressed beams and unstressedshell elements share many nodes. Therefore, still another approach canbe used.

In still another approach to modeling elastic members, the elasticmember 32 is modeled as a series of pre-contracted beams 44 along theedge of the elastics, as shown in FIG. 13. These beam elements allow forlinear extension and contraction in the stretch direction. To aid instability, a series of connecting beam elements 46 are created thatconnect the two beams 44. The resulting structure resembles a ladderalong the elastic, and is called a “laddered beam.” For contact purposesshell elements can be used, but a *MAT_NULL material model, availablefrom LS-Dyna is used so that the shells can be used in contact butprovide no structural support. In this approach the beams are allassigned a Young's modulus of 70 psi. The pre-stressed beams areassigned an initial principal stress of 52.5 psi in the stretchdirection and 0 psi in the other principal stress directions, for 75%pre-stretch.

However, the laddered beam approach can result in a higher probabilityof the elastics twisting during application to a virtual body, as shownin FIG. 14. To resolve this issue, one can replace the *MAT_NULL of theshell elements with a linear elastic material model, each available fromLS-Dyna. In one embodiment a material modulus of only 5 psi was used tomaintain the beams as the main structural components of the legelastics.

However, in some simulations it was observed that there were contactissues between the shell element and body of the garment wearer,especially in the waist elastics where the elastic nodes contact shellelements on the body that are significantly larger. Therefore, stillanother approach can be used. In another embodiment the cross beams 46are removed. The elastic shells are made linearly elastic with anelastic modulus of 70 psi, which is the same as the non-pre-contractedleg elastic. The pre-stretch was maintained at 75%, meaning the initialprincipal stress in the stretch direction was 105 psi. By keeping bothlinearly, substantially-parallel beams in a pre-stretched condition andshell elements with an increased modulus, pre-contraction of theelastics can be maintained, and the on-body fit is more realistic, asshown in FIG. 15.

Those skilled in the art will recognize that while the discussion hasfocused on using a null material and linear elastic material, a varietyof other properties are quite suitable for these purposes includingelastic-plastic, hyper-elastic, visco-elastic, membrane elements, amongmany others. The above-disclosed techniques and materials are useful formodeling extruded strand elastics and scrim materials.

Another structure than can be modeled in a virtual simulation is elasticmaterials in the form of webs or films. To model generally flat, elasticmaterials, the model can comprise solid elements to represent varyingsection thickness in elastic films. Elastic films can include aperturedformed films such as the formed film disclosed in U.S. Pat. No.5,968,029, U.S. Pat. Nos. 6,410,129, and 5,993,432, each issued to Curroet al. Elastic films can also include printed elastics, hot-pinapertured elastics, monolithic, monolithic, multilayer, perforated, andextruded elastic structures such as generally flattened scrims orstrands. When load conditions are substantially uniform, such elasticstructures can be represented as unit/repeatable cells along lines ofsymmetry to model fundamental stress/strain, contact, responses inproduct and process conditions.

Micro-structure beam or shell elements can be utilized to representvarying section thicknesses in thin films and in films havingthree-dimensionality, such as apertured formed films. The term“micro-structure” refers to geometrical features that are less than amillimeter in any direction and are most conveniently described in theunits of micrometers (microns). In the case of varying section thicknessin a film (i.e., varying caliper), the thickness at each node can bespecified and the average of the nodes that make up an individualelement can be assigned as the section thickness. In this manner thecomputational efficiency and stability for varying section structures isprovided.

When load requirements are governed by non-uniform conditions such ascontact with asymmetric bodies (e.g. baby hip, pudendal region, ornonlinear tool path), asymmetric load distribution (e.g. laminates ofvarying local section properties), the elastic structures can berepresented as a patterned unit cell on the feature to modelstress/strain, contact, responses in product and process conditions.

Another structure that can be modeled in a virtual simulation is a fold,or pleat in a thin, flexible material. For example, a topsheet on adisposable absorbent article may have a longitudinal fold or pleat topermit excess material for expansion of the absorbent core within. Inone embodiment, a fold or pleat can be made in a topsheet that isconnected to a secondary topsheet and a backsheet. The fold or pleatwould permit the topsheet and secondary topsheet to move independentlyof an underlying core, for example, which can be joined to a backsheet.As shown in the simple schematic in FIG. 16, a topsheet 50 can be joinedto a secondary topsheet or other acquisition or distribution material52, which can be independently moveable with respect to an underlyinglayer, such as absorbent core 54. The absorbent core can be joined to abacksheet 56, which is joined about an edge 58. The distances denoted asX and Y can be adjusted to give a total path length of excess material.In a virtual model, the fold or pleats can be modeled as shell or beamelements 60 and 62. In one embodiment the shell elements have no bendingstiffness, but do have tensile properties, commonly referred to asmembrane elements 64 and 66.

Another feature of products to be worn on the body is a series of foldsor pleats, such as corrugated or ring rolled portions of thin, flexiblematerials. Folds or pleats can be parallel. Ring rolling is a processknown in the art for making extensible materials, and involvesprocessing a web material between the nip of two counter-rotatingrollers having intermeshing teeth and grooves to produce folds, pleatsor other residual deformations. Material that can be extended by way ofunfolding in a direction perpendicular to the direction of thecorrugated or pleated portions can be modeled as a material having avery low tensile modulus until a certain extension is reached, at whichpoint unfolding is complete and the tensile modulus increases sharply.By tensile modulus is meant the slope of the tensile stress-strain curveat any given point along the curve.

As shown in FIG. 16, one model involves a plurality of generallyparallel pleat elements 72, each pleat element having at least one shellelement 68 and at least two membrane elements 70. Each pleat element canshare nodes with each adjacent pleat element along a common edge, asshown in FIG. 16. Further, each membrane element can share nodes witheach adjacent shell element along a common edge. As the material isstrained in a direction F, as shown in FIG. 16, the pleat elements willbe extended. Since the membrane elements carry little or no stiffness inbending, they contribute little or no additional stress to the materialuntil the membrane elements approach a co-planar relationship to theshell elements, at which time the membrane elements contribute to anincrease in tensile modulus of the pleat element. The amount of stretchprior to the region of increased modulus can be determined by thelengths A and B, or any additional lengths modeled. Because the membraneelements 70 can be pleated only in a single direction (perpendicular tothe preferred direction of stretch), if a force is applied in adirection parallel to the pleat direction (and in the plane of thepleats), the membrane and elastic material will be stretched (withoutbending or unfolding) based on their material properties, which is thebehavior replicating the actual behavior of pleated or ring rolledflexible webs.

Beam elements with no bending resistance, sometimes called a trusselement can be used instead of membrane elements in a model for pleats.Trusses can be used to model mechanical behavior of materials or productfeatures that have undergone pleating by the method known as ring-rollactivation. Truss elements can be aligned in the direction of thetooling where the truss represents the unactivated component of theprocessed portion of the structure. Every other node along a line ofconnected trusses is tied or bonded to the laminate so that theunprocessed portion can buckle in compression and carry load in tension.

Also, it is not necessary that the pleats be parallel to one another.Pleats can be modeled in which the folds make a fan shape, or othernon-linear, non-parallel arrangement.

Another feature that can be modeled is folds in a product to be worn onthe body. In particular, folds that are put in during manufacture canaffect the fit and comfort of a product when worn. Products that arefolded in packaging and unfolded for wear can be difficult to use if,once unfolded, the product tends to want to return to the foldedposition. By way of example, sanitary napkins are often folded andpackaged for discrete portability. For use a woman unfolds the sanitarynapkin for generally flat placement in her undergarment. If the sanitarynapkin tends to return to a folded configuration, placement can behindered. Once placed, the tendency to fold back can affect wearingcomfort and fit.

Sanitary napkins can be folded by what is referred to as “tri-folding,”in which the sanitary napkin is folded in thirds upon itself at two foldlines to fit into a smaller, relatively discrete package. The packagecan be flexible film, and can be attached to the release paper over thepanty fastening adhesive, such that removal of the wrapper also removesthe release paper.

FIG. 17 shows a virtual model of a sanitary napkin being folded. At step“A” the sanitary napkin is shown in its as-made flat condition. Asshown, sanitary napkin 72 can have a backing such as a film wrappermodeled as backing 74 and channels, grooves, embossments, or otherthree-dimensional features, 76. At step “B” the sanitary napkin isfolded slightly, and it can be seen in the virtual model that fold linesstart to appear. With more folding, as in step “C” the fold lines aremore pronounced.

FIG. 18 shows the same sanitary napkin model from FIG. 17 beingunfolded. As shown moving from step “A” to step “C” the sanitary napkincan be virtually unfolded to a flat condition. But, as shown in step “C”the fold lines remain, that is, virtual fold lines qualitatively appearon the unfolded modeled sanitary napkin.

To show how the fold lines 80 that remain in the unfolded sanitarynapkin 72 affect fit, the sanitary napkin can be virtually applied to abody, such as a body having a prescribed motion volume 26 and adeformable volume 22, as described above. The sanitary napkin 72 can beapplied to a garment 80 in a flat configuration as shown in FIG. 19A,and then the garment can be applied to the body as shown in FIG. 19B.Compression or other movement can be applied to the sanitary napkin bymoving the virtual body model to result in the deformation of thesanitary napkin as shown in FIG. 19C. As shown, the fold lines 78 can bequalitatively observed for effect on fit. In the virtual model, strainscan be correlated to stresses, which can in turn be correlated tocomfort of the garment, or the garment/sanitary napkin system.

When folds are modeled as above, it is possible to use the stresshistory, including residual stresses, in a subsequent step. For examplein the folding illustrated in FIG. 17 the stress history of the foldedsanitary napkin can be used when conducting the unfolding in FIG. 18.Alternatively, the stress history can be ignored in the unfolding step.Further, the stress history from either the folding and/or the unfoldingstep can be utilized in the step of applying to a garment/body system,as shown in FIG. 19.

Modeling involving folds can be used for other folded features as well,such as modeling residual stresses or residual deformations of foldlines, modeling folding and unfolding of wings of sanitary napkins,modeling folding and unfolding a diaper, folding and unfolding foldeditems such as maps, wallets, undergarments, and the like.

All documents cited in the Detailed Description of the Invention are, inrelevant part, incorporated herein by reference; the citation of anydocument is not to be construed as an admission that it is prior artwith respect to the present invention.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

1. A virtual model for simulating physical deformation of at least aportion of a product to be worn on a body, said portion comprising athin, flexible material, wherein said thin flexible material is modeledas having at least a first zone comprising bending properties, said zonecomprising bending properties modeled as micro-structure beam or shellelements.
 2. The virtual model of claim 1, wherein said thin flexiblematerial is modeled as having a second zone of contact and compressioncomprising at least one layer of three dimensional solid elements. 3.The virtual model of claim 2 in which said contact and compression zoneis modeled as at least one layer of three dimensional solid elementsdefining at least two major surfaces, wherein at least one of said majorsurfaces is said first zone.
 4. The virtual model of claim 2, whereinsaid solid elements comprise a plurality of elements joined to adjacentelements by at least one node to define a continuous structure.
 5. Thevirtual model of claim 1, wherein said thin flexible material is afibrous material.
 6. The virtual model of claim 1, wherein said thinflexible material is an absorbent material.
 7. The virtual model ofclaim 1, wherein said thin flexible material exhibits sided bendingbehavior.
 8. The virtual model of claim 1, wherein said major surface isan external major surface.
 9. The virtual model of claim 1, wherein saidmajor surface is an internal major surface.
 10. The virtual model ofclaim 1, wherein said product is a disposable product.
 11. The virtualmodel of claim 11, wherein said product is a disposable diaper.
 12. Thevirtual model of claim 11, wherein said product is a sanitary napkin.13. The virtual model of claim 11, wherein said product is a thermalwrap.